It is known to configure data storage devices to record binary data on magnetic media, this being known as magnetic encoding. A commonly used magnetic medium comprises a magnetic coating on a flexible structure configured for example in the form of a tape. Data is thereafter recorded by the process of magnetic encoding of tracks on the coating in accordance with a particular tape format. The format of information actually recorded on magnetic tape is termed the tape format and allows a suitably configured data storage device to recognize, control and verify the data. Modem tape formats known to those skilled in the art include Linear Tape Open format (LTO) and Digital Data Storage (DDS) format for example and a given data storage device utilizing, for example, LTO format may suitably be termed a Linear Tape Open format data storage device. Such an LTO data storage device having a drive mechanism, and a linear tape data storage medium stored on a removable cartridge, may suitably be configured with a buffer for buffering the data received from a host device prior to storing the received data on the magnetic tape. Similarly, the buffer is used to enable the stored data to be read from tape such as, for example, in cases of backing up a failed computer system. The former operation is known as a data back-up and the latter operation is known as a restore. A data storage buffer of the type discussed may suitably be configured of Dynamic Random Access Memory (DRAM) where the logic state to be entered in each cell is stored as a voltage on the small capacitance associated with a given transistor.
It has been found that data stored in DRAM's may be corrupted resulting in a data error. Two types of DRAM data error are known and may be defined as follows. A hard error is a data error due to a physical defect in the DRAM whereas a soft error may be defined as an error occurring through storage of a particular pattern of data, the pattern for some reason causing one or more bits to flip erroneously from one to zero or vice versa. Although corrupted data occurring through a softer error has been found to be relatively rare it is a serious problem for obvious reasons. Some DRAM's from some manufacturers have been found to cause soft errors of the type discussed above. The problem is particularly serious in data storage devices utilizing DRAM since data obtained from one or more hosts is typically first stored in a DRAM buffer whereafter the data is written onto a magnetic tape for example. The data stored on magnetic tape is therefore expected to be a true back-up of the data obtained from the host, but in fact may comprise corrupted data.
Until manufacturers of DRAM chips create some sort of inbuilt parity check, presumably implemented through automatic creating of parity, storing the parity created and checking the parity when the data is read out, then the problem of soft error corruption in DRAM's must be dealt with in some other way.
The problem is compounded in that frequently memory space is limited in data storage buffers such as DRAM storage devices and therefore methods such as storing data twice on the same DRAM or storing data twice utilising additional DRAM's is unfeasible for many applications. Adding parity or checksums suffers from similar problems.
In view of the above there is therefore clearly a need to provide a method and apparatus for protecting against soft errors in data storage device memory buffers and in particular in DRAM's.